When it comes to home and commercial security basics, sensors and monitoring are two of the most important components you should know about. At a minimum, security systems for homes, offices and industries include door sensors for exterior doors, window sensors to cover windows, gas sensors to detect gas leaks, and motion sensors to detect motion.
Passive Infrared (PIR) Motion Sensors:
For any home or commercial security system, “Passive Infrared (PIR)-based motion detectors” have become very popular in intrusion detection. They can be put for use in keyholes, kitchens, hallways, stairways and safe cabinets. PIR sensors work entirely by detecting the heat energy emitted by all objects above absolute zero temperature in the form of infrared radiation. This happens when an object passes in front of the background, such as a wall. The sensor senses a temperature change at that point in the sensor’s field of view from room temperature to body temperature, and then back again. The change in the incoming infrared radiation leads to a change in the output voltage, triggering the detection.
More commonly, PIR motion detectors use a microcontroller to perform the decision analysis. Apart from built-in ADC and signal conditioning, they also come along with hardware and software stacks required for the motion-sensing applications, leading to low component count and cost. A CMOS imaging sensor is needed to take a snapshot of the moving object in front of the PIR sensor, which is then transmitted over wired or wireless medium. The design of a PIR-based motion detector requires the sensor’s output signal to be amplified to become usable for a microcontroller or other discrete components. A differential amplifier can do differential detection to prevent false triggering due to brief flashes of light and nearby electric fields. A microcontroller can perform reliable decision-making to detect human motion and prevent false triggering by combining many control algorithms. A relay is often needed to raise an alarm in burglar alarm systems. Typically, an ambient light sensor detects and disables false alarms by turning ON and OFF of HVAC systems and flashing lights, thereby incorporating “White Light Immunity”. An anti-mask feature helps detect if something is placed in front of the detector, blocking its ability to detect motion.
For those who want to get a detailed walk-through of the design of PIR-based sensors, the following reference designs can help, which discuss how these sensors are employed in security systems along with their complete documentation:-
- Flexible PIR Intrusion Motion Detector; This reference design from Zilig demonstrates a flexible Passive Infrared (PIR)-based solution for a range of intrusion motion detection applications. The design centers on a ZMOTION Intrusion MCU from Zilog which handles all functions related to the operation of the detector. The MCU comes preprogrammed with motion detection algorithms always running in the background. The motion detection algorithms take advantage of the on-chip sigma/delta ADC to which the pyroelectric sensor is connected. A Clare CPC1017 Solid State Relay provides the alarm outputs. An anti-mask feature detects if something has been placed in front of the detector preventing it from detecting motion. More on this Reference Design
- Low-cost Wireless PIR Motion Detector: Here is a reference design from Atmel which meets low power, cost and size requirements for development of a Passive Infrared (PIR) motion detector. The design is built around the Atmel’s SAM4S MCU ideal for this application with ready to use hardware and software blocks. The MCU integrates an interface to read data from a CMOS digital image sensor and store images in internal or external memory. It is also able to do JPEG image compression in software for transmitting images to optimize transmission time and power consumption. This eliminates the need of highly priced CMOS imaging sensors with embedded JPEG compression. Further simplification in the design is achieved by low-power analog comparator or analog-to-digital converter for motion detection and low-power modes reducing the component count, size and cost. More on this Reference Design
- PIR Motion Detector with 4m Range: The reference design is a PIR motion detector that can detect a motion of a human with a mass of 50kg or greater from distance of 4m. The design based on a RL78/G1A low-power MCU uses an external analog front end. A test design procedure is provided to test the motion velocity sensitivity of the motion detector. The detector is allowed to alarm from any movement of the Human subject, but can’t do so for motion velocities less than 0.05 m/sec or greater than 5m/sec. Fluorescent or CF lighting outside the 3 meter radius of the sensor can’t trigger the PIR sensors. The design targets to achieve less than 42.8uA average current drain in standby mode with no motion in the field of sensor detection. More on this Reference Design
Sophisticated ‘gas sensor systems’ are being used in medical diagnostic, manufacturing processes, photo-voltaic systems, refineries, vehicles, homes and waste-water treatment systems. They are important to monitor and warn of a dangerous gas level which can be harmful to organic life. Gas detectors can be used to detect combustible or toxic gases. Generally, catalytic and infrared sensors detect combustible gases and electrochemical and metal oxide semiconductor technologies detect toxic gases. For reliable detection of toxic gases like carbon monoxide, chlorine and nitrogen oxides, highly sensitive electrochemical sensors are most commonly employed. Requiring very small amounts of operating currents, they also come with high resolution under one part per million (ppm) of gas concentration. This makes them well-suited for portable, battery powered instruments.
Modern gas detectors employ a microcontroller with a gas sensor to measure the concentrations of gas in their vicinity. A sensor identifies a gas by measuring the voltages at which it breakdowns which is characteristic of a specific gas. This is generally achieved by employing a highly integrated microcontroller with on-chip peripherals such as a high-resolution analog-to-digital converter, analog front ends, and wireless connectivity. Battery-powered, portable detectors can be worn around clothing and are designed by using very low-power gas sensors and microcontrollers. Some sensors can identify several gases simultaneously by breaking up the component signals from a complex signal. Various manufacturers produce these detectors with a digital display and wireless connectivity.
Mentioned below are some reference designs of “Gas Sensors” for a detailed walk-through of their designs:-
- Micropower Toxic Gas Detector; This reference design describes a low power, battery operated, portable gas detector using an electrochemical sensor. The design uses an Alphasense CO-AX Carbon Monoxide sensor. Because of the circuit’s extremely low power consumption, two AAA batteries or a 2.3 V to 5.5 V power supply can power the circuit. The circuit provides reverse voltage protection, and the ADP2503 high efficiency, bu
ck-boost regulator regulates the input supply to the 5V required to power the sensor. To measure the gas concentration, a 16-Bit Sigma Delta ADC with On-Chip In-AmpAD7798 is utilized. A microcontroller with a high-resolution ADC can further reduce the circuit’s power consumption to increase the battery life up to one year. More on this Reference Design
- Smartphone-connected Multiple Gas Sensor: TI offers a Gas Sensor reference design which can be used to monitor gases like carbon monoxide (CO), oxygen (O2), ammonia, fluorine, chlorine dioxide and others in many applications including mining, household CO sensing, healthcare and industrial controls. The design adds a Bluetooth Low Energy (BLE) feature to connect to an iPhone or an iPad via an iOS application running on them. A CR2032 coin-cell battery runs the system. An analog front end (AFE) from TI, LMP91000, interfaces directly with the electrochemical cell and a BLE system on a chip CC2541 with 8051 MCU core. The targeted gas sensor can be replaced based on the application, while keeping the same analog frontend (AFE) and BLE design. More on this Reference Design
- Small & Reliable CO Detector using Electrochemical Sensor: This reference design from Zilog describes a reliable electrochemical CO sensor based on a Zilog’s Z8 Encore XP microcontroller (MCU) and the Sixth Sense ECO-Sure (2e) CO sensor. Two important on-chip peripherals of the MCU that help to implement the solution include a Transimpedance Amplifier and a sigma-delta analog-to-digital converter (ADC). The transimpedance amplifier amplifies the current variations produced by the CO sensor and sends them to the on-chip ADC. The on-chip integrated hardware of the MCU minimizes the board space with very few external components. The MCU implements a power management routine to conserve power. The design discusses the complete hardware architecture and firmware implementation of the CO detector solution. More on this Reference Design
- Carbon Monoxide (CO) Detector with Compact sensor: This design from Renesas provides a sensor board that detects CO level of 100ppm or higher with a RL78 microcontroller from Renesas and a CO sensor TGS5042-A00. The documentation includes complete schematics, code, BOM, layout and testing procedure for the board. An actual CO sensing test can be performed with the board using CO aerosol. A buzzer alarm sounds once the existence of CO is detected. More on this Reference Design
Glass breakage detectors:
A glass breakage detector ensures safety in buildings and homes simply by detecting illegal entry through glass windows and doors. The detectors generally use narrowband microphones to capture and analyze vibrations or acoustic signals produced during a glass breakage. The microphones are generally tuned to the frequencies of glass breakage which vary with the type of glass. Typical glass breakage detectors utilize a low-power microcontroller to perform the signal analysis in software. For more complex sound analysis such as frequency composition and peak values, several glass-break sounds are compared with the present profile using signal transforms such as DCT (Discrete Fourier Transform) and FFT (Fast Fourier Transform). A hardware filter is used to restrict the signal spectrum to a particular frequency. A glass breakage alert can be indicated by an onboard buzzer and an LED.
Let’s walk-through some reference designs of “Glass-breakage detectors” along with their complete documentation:-
- Robust Glass Break Detector: The reference design from Renesas is a robust Glass break detector with a low power operation. Based on a RL78/G1A microcontroller from Renesas, the detector comes with an external analog front end to perform glass breakage detection. A test procedure is provided to test the system for all extraneous, false glass break events such as hand clap, slamming door and foot stomp. The design targets to achieve less than 42.8uA average current drain. More on this Reference Design
- Glass-Breakage Detector With Long Battery Life : This reference design from TI describes a robust single-chip glass breakage detector which allows long battery life with low power consumption. The design is built around a low-power MSP430F2274 microcontroller which consumes as low as 50µA average current during monitoring mode. The design performs spectral analysis of a typical glass breakage signal to analyze frequency composition, peak content, and more. An onboard buzzer and an LED provide glass breakage alert. False triggering of the glass-breakage detector is prevented by including an extra thud detection stage for avoiding sound events similar to glass breakage. This reference design includes firmware, hardware design files & other documentation. More on this Reference Design